DE102007005287A1 - Process for the preparation of ammonium paratungstate tetrahydrate and a high purity ammonium paratungstate tetrahydrate - Google Patents

Abstract

A process for the preparation of ammonium paratungstate tetrahydrate by thermal treatment of ammonium paratungstate decahydrate in aqueous suspension is described. The resulting ammonium paratungstate tetrahydrate can be produced in high purity and with high yield. In addition, the manufacturing process is simple and energy-saving.

Description

The The present invention relates to a process for the preparation of Ammonium paratungstate tetrahydrate and ammonium paratungstate tetrahydrate with a very high degree of purity.

Ammoniumparawolframathydrate (hereinafter referred to as APW) are known intermediates for the Production of Tungsten Metal, Tungsten-Containing Catalysts or of tungsten-based hard materials, for example of tungsten carbides, or sputtering targets. For the last mentioned application a particularly high degree of purity of the APW is required.

The Production of high purity APW is basically via the acid or alkali or melt digestion of Tungsten-containing concentrates or tungsten scrap with attached Purification stages via precipitation processes and liquid-liquid extraction. The purified solution is usually by evaporation concentrated, eventually crystallizing APW.

To The prior art discloses tungsten ore concentrates (eg, scheelite, Wolframite) and W-containing scraps with soda and / or caustic soda open minded. The resulting Na-tungstate solution is over several Stages by precipitation or ion exchange process of Si, P, F, Mo, As, Sb, Bi, Co, etc. prepurified. Subsequently is via a liquid-liquid extraction using amine-containing organic phases, the sodium tungstate converted into ammonium tungstate solution. Out of this solution APW is produced via evaporation crystallization.

alternative is z. For example, in China or Uzbekistan the cleaning and conversion process of digestion solutions carried out by means of ion exchange resins. Be here Tungsten and molybdenum absorbed by an exchanger, whereas Impurities such as Si, P and As, remain in the raffinate. Subsequently is via a selective elution tungsten from molybdenum separated. From the tungsten-containing eluate APW is also about made an evaporation crystallization. Typical impurity levels of in this way manufactured APW products are in the example part Table 2.

On Products made by these routes typically have a degree of purity from 99.9 to 99.99% by weight (3-4 N).

Detailed descriptions of prior art methods of making APW are in the patent documents DE-AS 1,244,141 . DE-A-196 28 816 . DE-C-197 24 183 and US-A-4,115,513 , as well as in the publications " Anionexchange method for preparation of ammonium derivatives from soda solutions, Kholmogorov, Vaneeva, Yurkevich, Tsvetnye Metally (Moscow, Russian Federation) 7/1978, pp. 59-62 "," Use of extraction by amines during the preparation of ammonium paratungstate, Petrov, Maslenitskii, Davydova, Tsvetnye Metally (Moscow, Russian Federation) 3/1974, pp. 38-39 "," Zhang, Gong, Huang, Huang, Zhongnan Kuangye Xueyuan Xuebao (1990), 21 (4), 389-96 "," Preparation of Ammonium Paratungstate from a Sodium Tungstate Sodium Chloride Phase, Raddatz, Gomes, Carnahan, Rep. Invest, US, Bur. Mines (1988), RI 9165 "as well as in the book" TUNGSTEN Properties Chemistry, Technology of the Element, Alloys, and Chemical Compounds (ISBN 0-306-45053-4, 1999), Lassner, Schubert, pp. 184-212 described.

In typical processes of the prior art is W concentrate with Sodium hydroxide or soda digested and the resulting liquor is with the addition of Mg, Al salts and sodium hydrogen sulfide of impurities, like P, As, Si, V and Mo, prepurified. Subsequently, will the sodium tungstate solution via a liquid-liquid Extraction using an organic phase (eg containing 7-10% by weight of diisotridecylamine, 10% by weight of isodecanol, remainder: White spirit) and converted into ammonium tungstate solution. This solution is fractionally evaporated and the resulting APW separated, washed and dried. Typical contamination levels of an APW product prepared in this way are in the example part Table 1.

One big disadvantage of the previously known methods is that the degree of purity of the products produced therewith for special applications, such as For sputtering targets, not enough. In addition, the APW manufacturing costs are due to the high energy consumption of the evaporation crystallization very high.

Based on this prior art, it is an object of the present invention, a wirtschaftli to provide a method which allows to produce a high purity ammonium paratungstate tetrahydrate with high product yield in a simple process.

A Another object of this invention is to provide a Ammonium paratungstate tetrahydrate with very high purity.

The invention is based on the surprising finding that ammonium paratungstate decahydrate ("APW decahydrate") in aqueous suspension quantitatively converts to highly pure ammonium paratungstate tetrahydrate ("APW tetrahydrate") by heating the suspended APW decahydrate. Preferred process parameters are the mass ratio of APW decahydrate to the aqueous solution, the NH ₃ concentration of the resulting aqueous solution, the NH ₃ : W molar ratio of the resulting aqueous solution, and the temperature of the thermal treatment.

The The present invention relates to a process for the preparation of Ammonium paratungstate tetrahydrate by conversion of aqueous phase suspended ammonium paratungstate decahydrate by heating in ammonium paratungstate tetrahydrate.

When Starting material for the inventive Method can be any prepared APW decahydrate be used.

In the priority same patent application with the internal reference STA 066009 a process for the preparation of coarsely crystalline APW decahydrate is described. According to this method, APW is prepared by re-extraction of a tungsten loaded organic phase with aqueous solution containing ammonia. By selecting suitable process parameters, it is possible to prepare a coarsely crystalline APW directly at the reextraction step. This can be crystallized in high purity and with high yield. In addition, the manufacturing process is simple and energy-saving. Under ammonium paratungstate hydrate in the sense of the description of this priority same patent application are the tetrahydrate, ie (NH ₄ ) ₁₀ [H ₂ W ₁₂ O ₄₂ ] × 4 (H ₂ O), and the decahydrate, ie (NH ₄ ) ₁₀ [H ₂ W ₁₂ O ₄₂ ] × 10 (H ₂ O), to be understood. The formation of these hydrates takes place as a function of the temperatures during the reextraction. The products available with the method of the priority same patent application have a relatively high degree of purity, eg. B. of> 4 N on. The yield of the crystallization step, based on the W content of the charged organic phase, is> 96%. For special applications, however, this degree of purity is not enough.

in the Process of the present invention is preferred as the APW decahydrate that according to the one in the same priority Application STA 066009 described method produced product used.

It is an ammonium paratungstate decahydrate prepared directly by re-extraction of a tungsten-loaded organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus, reextraction at an NH ₃ : W molar ratio of 0.83 1.30, preferably 0.85 to 0.95, and at a volume metering ratio of the tungsten loaded organic phase to the ammonia-containing aqueous solution of 5 to 25, preferably 10 to 15, was performed.

Prefers is an ammonium paratungstate decahydrate prepared by this process, during its production, the reextraction in the mixer is carried out in this way that a solids concentration of the ammonium paratungstate hydrate, based on the ammonia-containing aqueous phase in Mixer, from 100 to 1200 g / l, more preferably 500 to 800 g / l, established.

Also Particularly preferred is a produced by this method Ammonium paratungstate decahydrate, when produced in a blender the stirring speed is adjusted so that a non-homogeneous distribution of organic phase and ammonia-containing aqueous phase is achieved in the mixer.

In a further particularly preferred embodiment, an ammonium paratungstate decahydrate prepared by this process is used, the separation of the phase mixture being carried out in a stirrer-equipped settler with stirring, the speed of the stirrer being adjusted such that the organic phase entrained in the sedimentation of the ammonium paratungstate hydrate is separated, wherein the phase mixture from the mixer preferably in the phase boundary region between the organic phase and ammonia-containing aqueous phase of the settler is initiated.

In a further particularly preferred embodiment, an ammonium paratungstate decahydrate is used, which consists of at least 75% of crystals having a length of at least 200 microns, having a ratio of length to width of less than 4.5: 1, preferably a product containing a Bulk density of at least 1.7 g / cm ³ , preferably 1.8 to 2.2 g / cm ³ , having.

Especially becomes a suspended ammonium paratungstate decahydrate product used, which consists of at least 75% crystals with a length from 200 to 1000 μm, preferably from 300 to 400 μm, which has a length to width ratio of 3.0: 1 up to 3.5: 1.

In a further preferred embodiment of the invention Process is called aqueous phase or as an ingredient the aqueous phase to suspend the ammonium paratungstate decahydrate Ammonia- and tungsten-containing solution and / or deionized Water used, preferably the mother liquor and / or the wash water from the preparation of the ammonium paratungstate tetrahydrate and / or the mother liquor and / or the wash water from the production of Ammonium paratungstate decahydrate most preferably the mother liquor and / or the wash water from the preparation of the ammonium paratungstate decahydrate from that in the priority same patent application STA 066009 described method.

The NH ₃ concentration of the mother liquor in the preparation of the ammonium para tungstate tetrahydrate is preferably set between 1.5 to 12 g / l of NH ₃ , more preferably 2.0 to 4.0 g / l of NH ₃ .

The NH ₃ : W molar ratio in the mother liquor of the preparation of the ammonium paratungstate tetrahydrate is preferably adjusted to between 0.5 and 1.8, more preferably between 0.6 and 1.0.

NH ₃ concentrations and NH ₃ : W molar ratios outside the specified ranges lead to the incorporation of impurities into the product.

In addition, the differential scanning calorimetric spectrum (DSC spectrum) of the resulting product has an endothermic peak at NH ₃ concentrations of more than 12 g / l in the temperature range between 280-340 ° C.

The Mass ratio of APW decahydrate to aqueous Phase is preferably between 0.2: 1 to 2.5: 1, more preferred between 1: 1 to 1.8: 1.

at Mass ratios below the specified range deposits are formed on the reactor walls. A mass ratio above the specified range leads to deterioration the product purity.

The thermal treatment of the aqueous suspension of the APW decahydrate occurs at temperatures and durations that are sufficient to convert the APW decahydrate into APW tetrahydrate.

Prefers are temperatures of at least 65 ° C, particularly preferred from 85 to 95 ° C.

at Temperatures below 65 ° C does not produce a pure phase APW tetrahydrate. The highest product purity is in the reached preferred temperature interval.

The Duration of the thermal treatment must be sufficient in order to selected temperature the APW decahydrate completely into the APW tetrahydrate. typical Treatment times are in the range of 0.1 to 6 hours.

The Invention also relates to a novel ammonium paratungstate tetrahydrate, that a degree of purity of at least 99.999%, in particular a Purity of at least 99.9997%, based on the total mass of the product. Products with these degrees of purity are not yet described. Such products can be prepared by the method described above.

The novel ammonium paratungstate tetrahydrate of the present invention also differs from the prior art in that in the differential calorimetric analysis (DSC analysis, heating rate: 10 K / min) no endothermic reaction course in the temperature range between 280 and 340 ° C occurs. The diffe dimensional calorimetric characterization of the novel APW tetrahydrate in comparison to prior art products is disclosed in US Pat 1 shown.

In The following embodiments and figures will the invention described. A limitation on these examples and Figurines is not intended.

Embodiment 1

In a heated 200-liter stirred reactor 100 liters of ammonium and tungsten-containing solution with 3.5 g / l NH ₃ , 45.2 g / l W and 50 liters of deionized water were submitted. 200 kg of APW decahydrate were added with stirring. Subsequently, the suspension was treated for three hours at 85 ° C with stirring. The NH ₃ concentration of the liquid phase was 3.5 g / l at a NH ₃ : W molar ratio of 0.83: 1. The pH at room temperature was 6.9. The mass ratio between solid and aqueous solution was 1.14: 1. After the treatment, the suspension was filtered, the product was washed with 10 liters of demineralized water and finally dried at 100.degree. The product amount was 190 kg. This corresponded to a yield of 98.1%.

In Table 1 below shows the analytical data obtained of the product. Further, in this table, the analysis data becomes a commercially available APW tetrahydrate specified.

Embodiment 2:

In a heated 200-liter stirred reactor 215 liters of demineralized water were submitted. 200 kg of APW decay hydrate were added with stirring. Subsequently, the suspension was treated for two hours at 90 ° C with stirring. The NH ₃ concentration of the liquid phase was 2.1 g / l at an NH ₃ : W molar ratio of 0.77: 1. The pH at room temperature was 6.8. The mass ratio between solid and aqueous solution was 0.80: 1. After the treatment, the suspension was filtered, the product was washed with 10 liters of demineralized water and finally dried at 100.degree. The product amount was 184 kg. This corresponded to a yield of 95.3%. Table 1 shows the determined analysis data of the product.

Tabelle 2: Analysendaten von Produkten des Standes der Technik 1.) 2.) 3.) 4.) 5.) 6.) 7.) Al ppm 5 1 5 1 5 7 5 As ppm 10 4 10 7 7 5 11 Bi ppm 1 0,1 - - 1 0,5 < 1 Ca ppm 10 1 5 1 5 5 10 Cd ppm - - 5 - 1 - < 0,5 Co ppm 10 1 10 - 5 - 1 Cr ppm 10 1 10 1 5 - 7 Cu ppm 3 0,1 5 1 1 1 5 Fe ppm 10 3 10 1 10 6 12 K ppm 10 10 10 2 9 7 < 10 Mg ppm 7 1 5 1 5 7 < 1 Mn ppm 10 1 5 1 5 1 < 0,5 Mo ppm 20 7 30 6 20 14 27 Na ppm 10 5 10 5 9 8 < 10 Ni ppm 7 1 5 1 5 - 0,8 P ppm 7 5 7 7 5 7 12 Pb ppm 1 0,5 5 - 1 0,5 1 S ppm 7 7 7 - 5 - 0,02 Sb ppm 8 1 - - 2 - 0,4 Si ppm 10 3 10 1 8 6 8 Sn ppm 1 0,3 10 1 1 0,5 4 Ti ppm 10 3 10 - - - < 1 V ppm 10 3 10 - - - < 1 F ppm - - 25 - - - - Li ppm - - 5 - - - - Nb ppm - - 10 - - - < 3 Reinheit % 99,9823 99,9941 99,9776 99,9963 99,9885 99,9925 > 99,9868

• 1.) Chinese National Standard GB 10116-88
• 2.) Excellent Chinese Grade (Hegdu Tungstend)
• 3.) Specification Wolfram Bergbau und Hüttengesellschaft m. b. H.
• 4.) Osram Sylvania
• 5.) Fujan Xiamen Tungsten Products Plant
• 6.) Chinese Production, Jiangxi Province
• 7.) Muster: Alloys Plant Kirovgrad, Rußland

Table 2 shows analysis data of prior art products. Further, this table gives the analytical data of a commercial APW tetrahydrate.

Table 2: Analysis data of prior art products 1.) 2.) 3.) 4.) 5.) 6.) 7.) al ppm 5 1 5 1 5 7 5 ace ppm 10 4 10 7 7 5 11 Bi ppm 1 0.1 - - 1 0.5 <1 Ca ppm 10 1 5 1 5 5 10 CD ppm - - 5 - 1 - <0.5 Co ppm 10 1 10 - 5 - 1 Cr ppm 10 1 10 1 5 - 7 Cu ppm 3 0.1 5 1 1 1 5 Fe ppm 10 3 10 1 10 6 12 K ppm 10 10 10 2 9 7 <10 mg ppm 7 1 5 1 5 7 <1 Mn ppm 10 1 5 1 5 1 <0.5 Not a word ppm 20 7 30 6 20 14 27 N / A ppm 10 5 10 5 9 8th <10 Ni ppm 7 1 5 1 5 - 0.8 P ppm 7 5 7 7 5 7 12 pb ppm 1 0.5 5 - 1 0.5 1 S ppm 7 7 7 - 5 - 0.02 sb ppm 8th 1 - - 2 - 0.4 Si ppm 10 3 10 1 8th 6 8th sn ppm 1 0.3 10 1 1 0.5 4 Ti ppm 10 3 10 - - - <1 V ppm 10 3 10 - - - <1 F ppm - - 25 - - - - Li ppm - - 5 - - - - Nb ppm - - 10 - - - <3 purity % 99.9823 99.9941 99.9776 99.9963 99.9885 99.9925 > 99.9868

• 1.) Chinese National Standard GB 10116-88
• 2.) Excellent Chinese Grade (Hegdu Tungstend)
• 3.) Specification tungsten mining and metallurgical company mb H.
• 4.) Osram Sylvania
• 5.) Fujan Xiamen Tungsten Products Plant
• 6.) Chinese Production, Jiangxi Province
• 7.) Sample: Alloys Plant Kirovgrad, Russia

The data for 1) -6) are from " TUNGSTEN Properties Chemistry, Technology of the Element, Alloys and Chemical Compound (ISBN 0-306-45053-4, 1999), Lassner, Schubert, p. 210 ,

Embodiment 3

This example shows by means of in 2 apparatus described the preparation of inventive APW tetrahydrate. The inventive method is in a part of in 2 performed device shown.

W concentrate was digested with sodium hydroxide or soda and the resulting liquor under Zu Set of Mg, Al salts and sodium hydrogen sulfide of impurities such as P, As, Si, V and Mo, prepurified. As a further purification step of still contained anionic and cationic impurities, a liquid-liquid extraction using an organic phase (7-10% diisotridecylamine, 10% isodecanol, residual white spirit) was performed. The tungsten-loaded organic phase ("OP") was reextracted with NH ₃ solution. The device used for this purpose is in 2 shown.

In a with stirrer ( 2 ), Baffles ( 3 ) equipped mixing vessel ( 1 ) (also called container) (volume: 250 l, diameter: 600 mm, inclined blade stirrer: 6 blades, diameter: 300 mm, 4 baffles) were continuously via lines A, B and C 400 l / h W-laden OP and NH ₃ Solution is metered into the stirring area. Water was supplied via line B in order to adjust the NH ₃ concentration in a targeted manner. The W concentration of the OP and the NH ₃ concentration of the NH ₃ solution were automatically measured inline. The metering of the NH ₃ solution was automatically controlled by the NH ₃ : W molar ratio, which was fixed at 0.90. The OP / NH ₃ solution dosing ratio was set to 15: 1 and also automatically regulated by means of an additional water flow into the NH ₃ dosing line.

The volume flow of the OP was fixed. The volume flow of the NH ₃ solution was controlled as a function of the volume flow of the OP, the currently measured W and NH ₃ concentrations and the adjusted NH ₃ : W molar ratio. The H ₂ O volume flow was regulated as a function of the volume flow of the NH ₃ solution and the metering ratio of the reactants. The temperature in the container ( 1 ) Was adjusted to 48 ° C and controlled by the temperature of the educt solutions.

The transfer of the in the container ( 1 ) formed 3-phase mixture in the Settler ( 6 ) took place from the stirrer area of the container via the outlet ( 5 ) and line D and over the free overflow ( 4 ) of the container and line E. The stationary OP / AP ratio of 1/8 in the container ( 1 ), the emulsion type "oil in water", the steady state solids concentration of 250 g / l was over the stirrer speed (210 rpm), the phase mixture removal from the lower tank area (50 l / h) and the return of aqueous phase from the settler ( 6 ) in the container ( 1 ) (20 l / h). The residence time of the AP in the container ( 1 ) was 4.8 hours and the surgery 4.2 minutes. The phase mixture was mixed with a stirrer ( 7 equipped Settler ( 6 ) (Volume: 600 l, diameter: 750 mm (shape: conically tapering from half height; equipped with stirrer of the type of wall-mounted armature (inclined)). The stirrer speed of the settler ( 6 ) was set to 15 upm. The discharged OP was separated via the overflow of the settler via line F, washed with water and returned to the loading stage of the liquid-liquid extraction. The product suspension having a solids content of 1314 g / l was removed from the bottom of the settler ( 6 ) via line G into a stirrer ( 9 ) and baffles ( 10 ) equipped intermediate container ( 8th ), in which the method according to the invention was carried out. This intermediate container ( 8th ) thus contained an aqueous suspension of ammonium paratungstate decahydrate crystals. The interior of the intermediate container ( 8th ) was heated. This resulted in conversion of the APW decahydrate into the APW tetrahydrate. This product was added as an aqueous crystallizate mixture via line H into the filter ( 11 ) and washed the APW × 4H ₂ O with a little water to displace the mother liquor. The product was discharged from the process via line I, finally dried at 60 ° C. and characterized.

The mother liquor with 35 g / l W and 7.0 g / l NH ₃ was removed from the filter ( 11 ) discharged via line J and added after separation of the NH ₃ to the digestion solution of the W concentrates.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 1244141 [0007]
• - DE 19628816 A [0007]
• DE 19724183 C [0007]
• - US 4115513 A [0007]

Cited non-patent literature

• Kovalovorov, Vaneeva, Yurkevich, Tsvetnye Metally (Moscow, Russian Federation) 7/1978, pp. 59-62 [0007] - Anionexchange method for the preparation of ammonium paratungstate from soda solutions.
• - Use of extraction by amines during the preparation of ammonium paratungstate, Petrov, Maslenitskii, Davydova, Tsvetnye Metally (Moscow, Russian Federation) 3/1974, p. 38-39 [0007]
• - Zhang, Gong, Huang, Huang, Zhongnan Kuangye Xueyuan Xuebao (1990), 21 (4), 389-96 [0007]
• - Preparation of Ammonium Paratungstate from a Sodium Tungstate Sodium Chloride Phase, Raddatz, Gomes, Carnahan, Rep. Invest, US, Bur. Mines (1988), RI 9165 [0007]
• - TUNGSTEN Properties Chemistry, Technology of the Element, Alloys, and Chemical Compounds (ISBN 0-306-45053-4, 1999), Lassner, Schubert, pp. 184-212 [0007]
• - TUNGSTEN Properties Chemistry, Technology of the Element, Alloys and Chemical Compound (ISBN 0-306-45053-4, 1999), Lassner, Schubert, p. 210 [0041]

Claims (15)

Process for the preparation of ammonium paratungstate tetrahydrate, characterized in that ammonium paratungstate decahydrate suspended in an aqueous phase is converted by heating into ammonium paratungstate tetrahydrate. A method according to claim 1, characterized in that in the resulting mother liquor, an NH ₃ concentration between 1.5 to 12 g / l NH ₃ , preferably 2.0 to 4.0 g / l NH ₃ , is present. Method according to one of claims 1 to 2, characterized in that in the resulting mother liquor an NH ₃ : W molar ratio of 0.5 to 1.8, preferably 0.6 to 1.0, is present. Method according to one of claims 1 to 3, characterized in that the mass ratio of ammonium paratungstate decahydrate to mother liquor is adjusted so that this between 0.2: 1 to 2.5: 1, preferably between 1: 1 to 1.8: 1. Method according to one of claims 1 to 4, characterized in that the suspended ammonium paratungstate decahydrate to a temperature of at least 65 ° C, preferably 85 to 95 ° C, heated. Process according to any one of Claims 1 to 5, characterized in that the suspended ammonium paratungstate decahydrate used is a product which has been prepared directly by re-extraction of a tungsten-loaded organic phase with an ammonia-containing aqueous solution in a mixer-settler apparatus, the reextraction at a NH ₃ : W molar ratio of 0.83 to 1.30, preferably 0.85 to 0.95, and at a volume metering ratio of the tungsten-loaded organic phase to the ammonia-containing aqueous solution of 5 to 25, preferably 10 to 15 , was carried out. Method according to Claim 6, characterized that the reextraction in the mixer is done so that is a solids concentration of the ammonium paratungstate hydrate, based on the ammonia-containing aqueous phase in Mixer, from 100 to 1200 g / l, preferably 500 to 800 g / l, sets. Method according to one of claims 6 to 7, characterized in that in the mixer, the stirring speed is set so that a non-homogeneous distribution of organic Phase and ammonia-containing aqueous phase in the mixer is reached. Method according to one of claims 6 to 8, characterized in that the separation of the phase mixture in a equipped with stirrer Settler below Stirring takes place and that the speed of the stirring device is adjusted so that entrained in the sedimentation of ammonium paratungstate organic phase is separated, wherein the phase mixture of the Mixer preferably in the phase boundary between organic Phase and ammonia-containing aqueous phase of the settler is initiated. A process according to any one of claims 1 to 5, characterized in that the suspended ammonium paratungstate decahydrate used is a product consisting of at least 75% crystals of at least 200 μm in length and having a length to width ratio of less than 4.5 : 1, preferably a product having a bulk density of at least 1.7 g / cm ³ , preferably 1.8 to 2.2 g / cm ³ . Method according to claim 10, characterized in that as suspended ammonium paratungstate decahydrate a product is used, which consists of at least 75% crystals with a Length of 200 to 1000 microns, preferably 300 to 400 μm, which is a ratio of length to width of 3.0: 1 to 3.5: 1. Method according to one of claims 1 to 11, characterized in that as the aqueous phase or as a component of the aqueous phase for suspension Ammonium paratungstate decahydrate Ammonia- and tungsten-containing Solution and / or deionized water is used, preferably the mother liquor and / or the wash water from the production of the ammonium paratungstate tetrahydrate and / or the mother liquor and / or the wash water from the preparation of the ammonium paratungstate decahydrate. Ammonium paratungstate tetrahydrate with a purity grade of at least 99.999%, in particular of a purity of at least 99.9997% based on the total mass of the product. Ammonium paratungstate tetrahydrate according to claim 13, characterized in that its differential calorimetric spectrum in the temperature range from 280 to 340 ° C no endothermal Peak has. Ammonium paratungstate tetrahydrate, characterized that its differential calorimetric spectrum in the temperature range from 280 to 340 ° C has no endothermic peak.